Question 18: Work, Energy and Power & Circular Motion

Question

A block of mass 25 kg is pulled along a horizontal surface by a force at an angle $45^{\circ}$ with the horizontal. The friction coefficient between the block and the surface is 0.25 . The block travels at a uniform velocity. The work done by the applied force during a displacement of 5 m of the block is :

Accepted Answer

Block travels with uniform velocity
So $\quad \mathrm{a}=0 \Rightarrow \mathrm{~F} \cos 45^{\circ}=$ friction
$$\begin{aligned}
& \frac{\mathrm{F}}{\sqrt{2}}=\mu\left[\mathrm{mg}-\frac{\mathrm{F}}{\sqrt{2}}ight] \
& \frac{\mathrm{F}}{\sqrt{2}}=0.25\left[25 	imes 9.8-\frac{\mathrm{F}}{\sqrt{2}}ight] \
& \Rightarrow \quad 1.25 \frac{\mathrm{~F}}{\sqrt{2}}=61.25 \
& \mathrm{~F}=\frac{61.25 	imes \sqrt{2}}{1.25}=49 \sqrt{2} \
& \mathrm{~W}_{\mathrm{ext}}=\mathrm{FS} \cos 45^{\circ} \
&=49 \sqrt{2} 	imes 5 	imes \frac{1}{\sqrt{2}}=245 \mathrm{~J}
\end{aligned}$$

Answer

490 J

Answer

970 J

Answer

735 J

Answer

245 J

Work, Energy and Power & Circular Motion

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